SnowFlake所生成的ID一共分成四部分：

1.第一位

占用1bit，其值始终是0，没有实际作用。

2.时间戳

占用41bit，精确到毫秒，总共可以容纳约69 年的时间。

3.工作机器id

占用10bit，其中高位5bit是数据中心ID（datacenterId），低位5bit是工作节点ID（workerId），做多可以容纳1024个节点。

4.序列号

占用12bit，这个值在同一毫秒同一节点上从0开始不断累加，最多可以累加到4095。

SnowFlake算法在同一毫秒内最多可以生成多少个全局唯一ID呢？只需要做一个简单的乘法：

同一毫秒的ID数量 = 1024 X 4096 = 4194304

这个数字在绝大多数并发场景下都是够用的。

import java.util.concurrent.ExecutorService;import java.util.concurrent.Executors;/** * Created by xfyou 2018/6/8 14:01. */public class SnowFlakeIdGenerator {    // The initial time(2017-01-01)    private static final long INITIAL_TIME_STAMP = 1483200000000L;    // Machine ID bits    private static final long WORK_ID_BITS = 5L;    // DataCenter ID bits    private static final long DATACENTER_ID_BITS = 5L;    // The maximum machine ID supported is 31, which can quickly calculate the maximum decimal number that a few binary numbers can represent.    private static final long MAX_WORKER_ID = ~(-1L << WORK_ID_BITS);    // The maximum datacenter ID supported is 31    private static final long MAX_DATACENTER_ID = ~(-1L << DATACENTER_ID_BITS);    // Sequence ID bits    private static final long SEQUENCE_BITS = 12L;    // The machine ID offset,12    private static final long WORKERID_OFFSET = SEQUENCE_BITS;    // The datacent ID offset,12+5    private static final long DATACENTERID_OFFSET = WORK_ID_BITS + SEQUENCE_BITS;    // The timestape offset, 5+5+12    private static final long TIMESTAMP_OFFSET = DATACENTER_ID_BITS + WORK_ID_BITS + SEQUENCE_BITS;    // Sequence mask,4095    private static final long SEQUENCE_MASK = ~(-1L << SEQUENCE_BITS);    // Worker ID ,0~31    private long workerId;    // Datacenter ID,0~31    private long datacenterId;    // Sequence,0~4095    private long sequence = 0L;    // Last timestamp    private long lastTimestamp = -1L;    public SnowFlakeIdGenerator(long workerId, long datacenterId) {        if (workerId > MAX_WORKER_ID || workerId < 0)            throw new IllegalArgumentException(String.format("WorkerID can't be greater than %d or less than 0", MAX_WORKER_ID));        if (datacenterId > MAX_DATACENTER_ID || datacenterId < 0)            throw new IllegalArgumentException(String.format("DataCenterID can't be greater than %d or less than 0", MAX_WORKER_ID));        this.workerId = workerId;        this.datacenterId = datacenterId;    }    public synchronized long nextId() {        long timeStamp = System.currentTimeMillis();        if (timeStamp < lastTimestamp)            throw new RuntimeException("The current time less than last time");        if (timeStamp == lastTimestamp) {            sequence = (sequence + 1) & SEQUENCE_MASK;            if (0 == sequence)                timeStamp = tillNextMillis(lastTimestamp);        } else {            sequence = 0L;        }        lastTimestamp = timeStamp;        return (timeStamp - INITIAL_TIME_STAMP) << TIMESTAMP_OFFSET | (datacenterId << DATACENTERID_OFFSET) | (workerId << WORKERID_OFFSET) | sequence;    }    private long tillNextMillis(long lastTimestamp) {        long timestamp = System.currentTimeMillis();        while (timestamp <= lastTimestamp)            timestamp = System.currentTimeMillis();        return timestamp;    }    public static void main(String[] args) {        SnowFlakeIdGenerator generator = new SnowFlakeIdGenerator(1, 1);        ExecutorService executorService = Executors.newCachedThreadPool();        for (int i = 0; i < 5; i++) {            executorService.execute(new Runnable() {                @Override                public void run() {                    long id = generator.nextId();                    System.out.println(id);                }            });        }        executorService.shutdown();    }}

 一个可能的输出为：

189783462515970048189783462515970049189783462515970050189783462515970051189783462520164352